The process of this invention relates to dyeing molded plastic articles containing predominantly urea formaldehyde resin or melamine formaldehyde resin. More particularly the process of this invention relates to dyeing buttons made predominantly of urea formaldehyde resin or melamine formaldehyde resin by a post-molding treatment.
Molded synthetic plastic articles like buttons, clock cases, display boxes, closures, electric razor housings, lighting fixtures and reflectors, tableware, electric wall plates, kitchen accessories and housewares of all types are produced in a variety of colors. These articles are colored by adding a dye to the synthetic plastic after it is molded or by adding a dye or pigment to the synthetic plastic while it is in a pre-molded form; i.e., a powdered form. When the molded synthetic plastic articles are made of polyester, methacrylate, polyamide, polystyrene and polyethylene, the dye may be added either before or after molding. For example, buttons molded from methacrylate and polyester are dyed after molding by a surface treatment with dispersion dyes. The buttons have a good to adequate dry cleaning fastness, iron fastness, rubbing fastness, water fastness and wash fastness. When the molded synthetic plastic articles are molded from urea formaldehyde or melamine formaldehyde, with or without a filler, the dye is usually added to the synthetic plastic material while it is in a pre-molded form. Only recently it has been suggested to dye synthetic plastic articles molded from urea formaldehyde resin after molding.
It has been suggested that buttons of pure urea formaldehyde resin can be dyed after molding with a specific acid dye. The buttons are immersed in a dye bath containing "Uresol" colorant (dye) in an amount in the range of 0.30 to 0.59 wt. % and "Urelux" fixer (stabilizer) in an amount in the range of 0.10 to 0.30 wt. % and acetic acid 80 to 85% in an amount in the range of 0.31 to 0.62 wt. % and water in an amount of 98.49 to 99.29 wt. %. The "Uresol" colorant and "Urelux" fixer are available from Synterge in Varese, Italy. The temperature of the dye bath should not exceed 60.degree. C. and preferably should be in the range of 50.degree. to 55.degree. C. The urea formaldehyde buttons dyed by the dye and process mentioned above do not have the best available detergent wash fastness.
Reactive dyes have been used for dyeing cellulosic fibers, wool, nylon, acetate, polyester fibers and leather. Amino-substituted dyes are readily associated with the dichlorotriazinyl group by reaction with cyanuric chloride. These dichlorotriazinyl dyes are very reactive with cellulosic fibers. This reaction with cellulose may occur by nucleophilic substitution or by nucloephilic addition. The former yields cellulose esters while the latter yields cellulose ethers. The dichlorotriazinyl dyes are applied to the cellulose fibers in an aqueous weakly basic or weakly acidic dye bath. This treatment is usually followed by a weakly alkaline after-treatment.
A series of dichlorotriazinyl dyes containing the dichloro-s-triazinyl amino group purportedly reacts with cellulose at a temperature around 20.degree. to 30.degree. C. in soda-alkaline, salt-containing bath. This series of dyes is commercially available from Imperial Chemical Industries Ltd., Manchester M93DA, England. These dyes which are used for textile dyeing are not recommended for use at a temperature above 70.degree. C. The manufacturer makes this recommendation because at temperatures greater than 70.degree. C. a competitive reaction of hydrolysis occurs in addition to the reaction between the dye and the cellulose. The hydrolysis reaction produces hydroxy derivatives that are no longer capable of reaction with cellulose.
Premetallized dyes in 1:1 and 2:1 complexes of organic moiety to metal have been used as dyes for wool, nylon and silk. The metal is usually chromium or cobalt. These dyes are known for their excellent light fastness. A neutral or slightly acid dye bath is used to apply these dyes to the fibers.
An object of this invention is to provide a process for the post-mold dyeing of molded synthetic plastic articles that contain predominantly urea formaldehyde resin or melamine formaldehyde resin.
A further object of this invention is to provide a process for the post-mold dyeing of buttons containing predominantly urea formaldehyde resin or melamine formaldehyde resin resulting in dyed buttons having good, even shades and excellent sublimation fastness and dry cleaning fastness, and satisfactory to excellent detergent and/or bleach wash fastness.